In some modern wireless communications systems a mobile station, such as a cellular telephone or wireless communicator, is enable to operate in two frequency bands. In a first frequency band the mobile station is able to make and receive calls through a conventional cellular network having base stations and a mobile switching network. In a second frequency band the mobile station is able to make and receive calls through a local or residential base station, also sometimes referred to as a personal base station. By example, when entering a building (such as a residence or an office) having a personal base station the mobile station automatically switches from the first frequency band to the second frequency band. Appropriate signalling and message formats are used to inform the telephone network that any calls to the mobile station should be routed to a telephone number associated with the personal base station. If an incoming call arrives the personal base station pages the mobile station over a paging channel and thereafter sets up the required voice channel, with the paging and voice channels both being in the second frequency band.
A problem that exists in presently specified systems relates to the occurrence of a failure of the primary power to personal base station, and/or an incoming telephone line failure. By example, as presently specified the personal base station is required to delay for some period of time (e.g., 15 minutes) after an occurrence of a line failure before terminating the RF carrier. As can be appreciated, during this time the mobile station may miss any incoming paging messages and, thus, may not receive an important incoming call.
Another problem that is not adequately addressed in currently implemented or proposed systems relates to the case where a conventional residential telephone shares the telephone line with the personal base station. If the residential telephone is in use, a call to the associated telephone number that is intended for the mobile station will receive a busy signal.